// newio/MappedIO.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.

import java.io.*;
import java.nio.IntBuffer;
import java.nio.channels.FileChannel;
import java.util.Arrays;

public class MappedIO {
    private static int numOfInts = 4_000_000;
    private static int numOfUbuffInts = 100_000;

    private abstract static class Tester {
        private String name;

        Tester(String name) {
            this.name = name;
        }

        public void runTest() {
            System.out.print(name + ": ");
            long start = System.nanoTime();
            test();
            double duration = System.nanoTime() - start;
            System.out.format("%.3f%n", duration / 1.0e9);
        }

        public abstract void test();
    }

    private static Tester[] tests = {
            new Tester("Stream Write") {
                @Override
                public void test() {
                    try (
                            DataOutputStream dos =
                                    new DataOutputStream(
                                            new BufferedOutputStream(
                                                    new FileOutputStream(
                                                            new File("temp.tmp"))))
                    ) {
                        for (int i = 0; i < numOfInts; i++)
                            dos.writeInt(i);
                    } catch (IOException e) {
                        throw new RuntimeException(e);
                    }
                }
            },
            new Tester("Mapped Write") {
                @Override
                public void test() {
                    try (
                            FileChannel fc =
                                    new RandomAccessFile("temp.tmp", "rw")
                                            .getChannel()
                    ) {
                        IntBuffer ib =
                                fc.map(FileChannel.MapMode.READ_WRITE,
                                        0, fc.size()).asIntBuffer();
                        for (int i = 0; i < numOfInts; i++)
                            ib.put(i);
                    } catch (IOException e) {
                        throw new RuntimeException(e);
                    }
                }
            },
            new Tester("Stream Read") {
                @Override
                public void test() {
                    try (
                            DataInputStream dis =
                                    new DataInputStream(
                                            new BufferedInputStream(
                                                    new FileInputStream("temp.tmp")))
                    ) {
                        for (int i = 0; i < numOfInts; i++)
                            dis.readInt();
                    } catch (IOException e) {
                        throw new RuntimeException(e);
                    }
                }
            },
            new Tester("Mapped Read") {
                @Override
                public void test() {
                    try (
                            FileChannel fc = new FileInputStream(
                                    new File("temp.tmp")).getChannel()
                    ) {
                        IntBuffer ib =
                                fc.map(FileChannel.MapMode.READ_ONLY,
                                        0, fc.size()).asIntBuffer();
                        while (ib.hasRemaining())
                            ib.get();
                    } catch (IOException e) {
                        throw new RuntimeException(e);
                    }
                }
            },
            new Tester("Stream Read/Write") {
                @Override
                public void test() {
                    try (
                            RandomAccessFile raf =
                                    new RandomAccessFile(
                                            new File("temp.tmp"), "rw")
                    ) {
                        raf.writeInt(1);
                        for (int i = 0; i < numOfUbuffInts; i++) {
                            raf.seek(raf.length() - 4);
                            raf.writeInt(raf.readInt());
                        }
                    } catch (IOException e) {
                        throw new RuntimeException(e);
                    }
                }
            },
            new Tester("Mapped Read/Write") {
                @Override
                public void test() {
                    try (
                            FileChannel fc = new RandomAccessFile(
                                    new File("temp.tmp"), "rw").getChannel()
                    ) {
                        IntBuffer ib =
                                fc.map(FileChannel.MapMode.READ_WRITE,
                                        0, fc.size()).asIntBuffer();
                        ib.put(0);
                        for (int i = 1; i < numOfUbuffInts; i++)
                            ib.put(ib.get(i - 1));
                    } catch (IOException e) {
                        throw new RuntimeException(e);
                    }
                }
            }
    };

    public static void main(String[] args) {
        Arrays.stream(tests).forEach(Tester::runTest);
    }
}
/* Output:
Stream Write: 0.615
Mapped Write: 0.050
Stream Read: 0.577
Mapped Read: 0.015
Stream Read/Write: 4.069
Mapped Read/Write: 0.013
*/
